1. Field of the Invention
The invention relates to a method for switching a relay with two current paths connected in parallel, as well as to the relay for carrying out the method.
2. Description of Relevant Art
In the photovoltaic industry, inverters are normally used to convert the direct current supplied by photovoltaic modules on roofs into alternating current. These inverters have a DC voltage input, a DC voltage intermediate circuit and an output AC voltage side for feeding the electrical power generated by the photovoltaic modules into the electricity grid. In order to be able to safely connect and disconnect the inverters on the input side as well as on the output side, i.e. to galvanically separate them from the grid or the photovoltaic system (or, respectively, to reliably conduct currents during operation, mechanical isolating switches are used for generating a galvanic isolation path). The isolating switches are usually realized in the form of relays which are mounted in the inverters directly on the circuit boards. In general, inverters comprise a controller, which controls the level of the output-side voltage and/or the power provided to the grid by the inverter. The controller also controls the relays as well as all other tasks for the operation of the inverter, like a reduction of fed-in power on behalf of an energy supply company. If the switch is closed, a load current can flow; otherwise not. Relays are switches that are switched by means of an actuator, usually by switching on and off an electromagnet, which causes a contact of the switch to change between at least two switching states (e.g. switch open/switch closed).
For this purpose, relays have a first contact which is movable relative to a second contact. The first contact typically has an elastic metal strip which is with one end attached to a carrier, such that the other end is movable. The movable end carries a first contact piece for contacting an opposing second contact piece. The first contact piece and the second contact piece are pressed against one another when the contact is closed. The second contact piece is attached to a conductive metal rail. The metal rail may be a rigid profile or it may be a spring-elastic metal strip. Each of the metal rail and the elastic metal strip is commonly also referred to as a contact finger or contact spring. The first contact finger and the second contact finger form a main contact together with the respective contact pieces. The contact pieces can be formed by, for example, rivets or as contact surface(s) welded onto the contact fingers. The contact pieces may include conductive materials such as copper, aluminum or brass.
With the actuator, the first contact can be moved to contact the second contact or to be separated from it. Resetting the first contact finger into its initial position may be performed by means of an additional spring, or it may be performed solely via the spring elasticity of the contact finger and/or the actuator.
Usually, an electrically controllable drive element is used as an actuator. Relays often have an actuator configured as a linear motor that includes, for example, a coil and an armature movably associated with the coil. With the coil switched on, a force acts on the armature which moves the armature. The movable armature is generally coupled to the movable first contact pieces or the associated contact finger such that they are moved with a movement of the armature.
In high-current applications, such as e.g. the aforementioned inverter, relays often have two main contact pairs connected in parallel, each having a first movable contact and a second contact, for increasing failure-safety or ampacity. Each of the four contacts has a contact piece which is positioned opposite to a complementary contact piece. A common actuator acts on the two movable contacts.